Recently, ion beam processing apparatus for repairing a pattern film, a mask and a semiconductor circuit formed on a substrate were disclosed in U.S. Pat. Nos. 4,930,439 and 4,876,112. When this apparatus is used for removing an undesired portion of a film, irradiation is repeatedly carried out while scanning with a focussed ion beam and thereafter the undesired portion is removed by sputtering. When a new film is formed at a portion which lacks a pattern with this apparatus, organic compound gas is applied selectively to the portion while scanning the portion repeatedly with an ion beam so as to condense the organic compound.
Conventionally, a gas gun such as disclosed in U.S. Pat. No. 4,930,439 is used for such ion beam processing apparatus. This gun includes a nozzle body which is inserted in a cylinder and can move back and forth. When the nozzle is moved forward, a gas exhaust passage in the cylinder which is connected to a compound supply source communicates with a gas exhaust passage in the nozzle. On the other hand, when the nozzle is moved backward, communication between the passage of the cylinder and the passage of the nozzle is broken. Accordingly, when the nozzle is moved forward, gas comes out of the head of the nozzle, and when the nozzle is moved backward, gas flow stops.
A valve provided between the passage from the gas supply source and the passage in the nozzle is driven separately to turn on and off the gas without moving the nozzle.
The above noted conventional gas gun has drawbacks as follows:
(1) The valve is opened and closed by the movement of the nozzle. Therefore, the nozzle is moved backward to carry out the steps of removing a film and scanning a certain area of a sample with a focussed ion beam to detect second charged particle and thereby observe the surface of the sample. On the other hand, the nozzle is moved forward for the step of forming a film. According to the change of the position of the nozzle, the electric field in the vicinity of the nozzle changes slightly, which causes a drift of the location of focussed ion beam irradiation at the sample surface.
(2) Conventionally, the distance between the nozzle head and the sample is around 0.5 mm. Therefore, it can often happen that the nozzle head hits the sample when moving or replacing the sample, and the sample and/or the nozzle head are damaged.